PLANT NUTRITION The soil and nutrients Essential mineral nutrients Nitrogen metabolism

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  • PLANT NUTRITIONThe soil and nutrientsEssential mineral nutrients Nitrogen metabolism

  • Plant Macronutrients(each may greatly exceed 1% dry weight of healthy plant)Carbon (CO2) [non-mineral.] carbs, lipids, proteins, nucleic acidsHydrogen (H2O) [non-mineral.] carbs, lipids, proteins, nucleic acidsOxygen (CO2, H2O) [non-mineral]carbs, lipids, proteins, nucleic acidsNitrogen (NO3-, NH4+ [non-mineral] proteins, nucleic acids...

    Phosphorus ( HPO4-, H2PO42-)nucleic acids, phospholipids, ATP...Potassium (K+) osmotic pressure; stomata opening, closingSulfur (SO42-) proteins, coenzymes...Calcium (Ca 2+) cytoskeleton; membrane perm. Magnesium (Mg2+)chlorophyll;

    Magnesium deficiciency in a tomato plant. Yellowing of leaves (chlorosis) is the result of an inability to synthesize chlroophyll, which contains magnesium

  • Plant Micronutrients(in most plants, each comprises from less than one ppm to several hundred ppm) Iron (Fe3+) cytochrome component; activates some enzymesManganese (Mn2+) amino acid formation, activates some enzymes,Copper (Cu2+) component of many redox and lignin biosynthetic pathwaysZinc (Zn2+) chorophyll formation; activates some enzymesMolybdenum (MoO43+) nitrogen fixation; nitrogen reduction Chlorine (Cl-) osmotically active; required for photosynthesisBoron (H2BO3, HBO32) cofactor in chlorophyll synthesisNickel (Ni2+) cofactor of nitrogen metabolism enzyme

    Copper-deficient plant with blue-green, curled leavesManganese-deficient plant with chlorosis (yellowing) between the veins

  • The role of soil in plant nutrition

  • SOIL HORIZONS IN ROADCUTSOIL FORMATIONMineral particles; millions of years of weathering of rocks by biological and physical processesOrganic material; decomposition of organic debrisSOIL COMPOSITIONSoil Highly weathered outer layer of Earths crust, consists of mineral matter and organic matterMinerals; elements bound as inorganic compoundsMineral matter; includes clay silt, sand, rock mineral sourcesOrganic matter; includes humus

  • Topsoil Mixture of broken-down rock of various texturesSubsoil Less organic matter, less weathering than topsoilWeathering bedrock Mostly partially broken-down rock parent material for upper layers SOIL HORIZONS IN ROADCUT

  • Most roots occur in the topsoil

  • Surface litter

    Top soil

    Sub soilBedrock

    FungusBacteriaProtozoaMiteSpringtailNematodeRootRoot nodules:nitrogen fixing bacteriaDiversity of Life in a Fertile Soil(Solomon 1999)

  • Soil ParticlesSoil AirSoil water with dissolved mineralsWet soil; most pore space is filled with waterDry soil; thin film of water is tightly bound to soil particles; water that percolates down through soil carries with it dissolved nutrients (leaching)Pore space, soil, air and water; the degree to which plants and soil organisms are sustained depends on the degree to which soils are moist and aerated(Solomon 1999)

  • Soil ParticlesSoil AirSoil water with dissolved minerals(Solomon 1999)Three of the most important gases in soil are: Oxygen (O2) required by soil organisms for aerobic respirationNitrogen (N2) used by nitrogen-fixing bacteria and Carbon Dioxide (CO2), a product of aerobic respiration

  • Solutes (dissolved, osmotically active molecules) cytoplasm membrane soilPlants acquire their nutrients and water primarily through their rootsWater potential is the pressure, created across a semipermeable membrane, that leads to the flow of water. Its the result of both osmotic pressure and water pressure differences.(Keaton and Gould 1993)

  • Nutrient uptake and availabilityMineral nutrients are exchanged as negative or positive ionsMany mineral nutrients exist in soil as positively charged ions (cations) bound to clay; clay particles have important role in nutrient uptakeMineral nutrients existing in soil as negatively charged ions are easily leached from soil

  • Plants are affected by soil pH for two main reasons:-solubility of certain minerals varies with pH-ability of soil to bind cations decreases with increasing soil acidityAtmospheric acid precipitation decreases soil pH (increases acidity)Solubility of three mineral nutrients as a function of pH (Keaton and Gould 1993)

  • Important Factors That Influence Soil pH

    Chemical composition of the soil and bedrock affects pH

    Cation exchange that roots perform decreases pH of soil

    Cellular respiration of soil organisms, including decomposers, decreases pH

    Acid precipitation sulfuric and nitric acids in atmosphere fall to ground as acid rain, sleet, snow, fog decreases pH

  • Llife on Earth depends on Nitrogen-fixation; carried out exclusively by certain Nitrogen fixing bacteria that reduce N2 to NH3 through reaction sequence mediated by one enzyme complex: nitrogenasePlants acquire nitrogen mainly as nitrate (NO3-), which is produced in the soil by nitrifying bacteria that oxidize ammonium (NH4+) to NO3- N2 + 8e- + 8H+ + 16 ATP 2NH3 + H2 + 16 ADP +16 P ireduction of N2oxidation of NH4

  • Throughout the chemical reactions of nitrogen fixation, the reactants are bound to the enzyme nitrogenase, a reducing agent that transfers hydrogen atoms to nitrogen to form the final product ammonia (picks up H+ in soil to form ammonium (NH4+)

  • Nitrogen Fixers

    Oceans various photosynthetic bacteria, including cyanobacteriaFreshwater cyanobacteria

    Terrestrial certain soil eubacteria Rhizobium bacteria living symbiotically in the root nodules of legume plantsNitrogen-fixing Cyanobacteria.

  • Nitrogen-fixing Cyanobacteria.

  • Cation ExchangeSolomon 1999